Project summary/abstract Nonsteroidal anti-inflammatory drugs (NSAIDs) have cancer chemopreventive activity, but are not recommended for long-term use because of toxicities resulting from cyclooxygenase (COX) inhibition. However, sulindac and its congener, indomethacin (indo) inhibit the growth and induce apoptosis of tumor cells in vitro and are potentially effective for treating malignant disease by mechanisms that appear to be unrelated to COX inhibition. The Piazza lab has identified a novel series of non-COX-inhibitory sulindac derivatives with potent tumor cell growth inhibitory activity by targeting cGMP phosphodiesterase (PDE) isozymes, PDE5 and/or PDE10 to induce cGMP signaling. MCI-030 is a prototypic non-COX-inhibitory sulindac derivative with selectivity for PDE10 inhibition and strong in vitro and in vivo anti-tumor activity. Collaborative efforts from the Zhou and Piazza laboratories discovered that sulindac, MCI-030, as well as a sulindac congener, indomethacin (indo) are capable of inducing ER stress in tumor cells and can sensitize lymphoma cells to T cells engineered to express CD19-targeting chimeric antigen receptors (CD19CAR). These findings establish the premise of our hypothesis that it is feasible to design and develop novel sulindac derivatives with potent tumor cell growth inhibitory and immunostimulatory activities by targeting PDE5 and/or PDE10. The objective of our study is to define the molecular and cellular mechanisms by which sulindac and its non-COX derivatives condition an immunogenic tumor microenvironment. Specifically, we will determine how sulindac and non- COX inhibitory derivatives induce cancer immunogenic cell death, mitigate Treg and MDSC- mediated immunosuppression, and activate dendritic cells via effects on tumor cells involving ER stress induction, and suppression of oncogenic ?-catenin, which we hypothesize are triggered by PDE5/10 inhibition (aim 1). We will test the effectiveness of sulindac and non-COX inhibitory derivatives that inhibit PDE5 and/or PDE10 in potentiating cancer immunotherapies including PD1 blockade and adoptive T cell therapy in multiple preclinical models (aim 2). Knowledge obtained from Aim 1 and 2 will be integrated into a synthetic chemistry campaign to develop new sulindac derivatives with improved antitumor activity by directly suppressing tumor cell growth and by indirectly activating antitumor immunity, without the toxicities associated with COX inhibition (aim 3). Successful completion of the project will pave the way for developing novel sulindac derivatives as immunomodulators for cancer treatment in the arena of cancer immunotherapies.